Electric resistance element and method of making same



July 5, 1938. R. G. BRIDGES 2,122,604

ELECTRIC RESISTANCE ELEMENT AND METHOD OF MAKING SAME Filed NOV. 29,1955 llm cn tor.

Wovymond G, Br/k/ es.

Patented July 5, 1938 UNITED I STATES ELECTRIC RESISTANCE ELEMENT ANDMETHOD or MAKING SAME Raymond G. Bridges, Toronto, Ontario, CanadaApplication November 29, 1935, Serial No. 52,0

6 Claims.

The principal objects of this invention are to devise a covering forelectrical conductors of various kinds which will present a veryeifective electrical insulation and will have exceptionally highresistance to moisture penetration and will,

when used as a covering for electric heating elements, permit a rapidtransfer of heat from the electric resistance member.

A further object is to provide an insulating covering which may be veryeasily and cheaply manufactured and may be easily and quickly installedin heating devices such as electric irons, hot plates, etc., and whencompleted will be of very high efiiciency.

The principal feature of the invention consists in the novel manner ofcovering an electrical conductor whereby a layer of dielectric materialis interposed between fabricated surfaces to fill in the intersticesbetween the fabricated strands 2 and coat the surfaces thereof topresent an effective resistance to moisture and the passage of electriccurrent and to form a strong and durable element highly efficient in thetransference of heat.

In the accompanying drawing, Figure 1 is a plan view showing my improvedheating element arranged in the base of an electric iron.

Figure 2 is a plan view of the heating element.

Figure 3 is a perspective view'illustrating the manner in which theinsulation is fabricated around an electric heating element.

Figure 4 is an exaggerated sectional elevational view showing thefabricated insulation on an electric conductor.

It has been previously proposed to manufacture a resistance element witha spirally coiled resistance wire surrounded by a braided, Woven orspirally wound fibre construction which may or may not be impregnatedwith a suitable resistance material which will not be seriously affectedby heat, and braided asbestos has been coated with various solutionswhich are then baked hard.

According to the present invention an electric heating coil orresistance wire I is preferably wound in an open mesh spiral coil andbraided over this coil is a covering 2 preferably made from threads ofasbestos fibre, which may however, be reinforced by a certain percentageof strong cotton threads.

' After the covering 2 has been braided over the coiled resistance wireinsulating or refractory material in a soft plastic or solution form isapplied to fill the interstices in the fabricated covering and form athin covering thereover.

Over this coating is braided a second covering 4 of asbestos and cottonfibres and as this covering is completed a thin coating of insulating orre,- fractory material is applied to fill the interstices in the fabricand form a thin outer coating.

The second fibrous coating 4 is applied over the top of insulatingmaterial 3 while it is in a moist condition, so that the threads embedthemselves in the soft material and the outer coating 5 is thoroughlyembedded in the outer surface of the outer fabricated covering.

A resistance element thus constructed is cut to the desired length and aterminal block 6 of a desired form is connected to the ends. The elementwhile still in a soft, plastic form, is preferably placed in a mouldprovided with means for shaping the element, fabricated as described, tothe desired conformation, and when so formed it is subjected to atemperature higher than that, which will be applied through theresistance member to fuse the refractory material to form a hard,moisture resistant element, which will, however, form an efficient heattransfer medium under the energy applied to the electric resistance.

It will be understood that in saturating or impregnating the firstcovering of fibrous material, then placing the second covering over thatand in turn saturating it with a refractory or dielectric material, thespaces between the asbestos fibres or cords will be very completelyfilled in and any voids left through the burning out of the cottonthreads in the fusing or baking operation will not impair the electricinsulating value. Further, the baking of the refractory material forms ahard, moisture-resisting shell which effectively prevents corrosion ofthe enclosed metallic resistance wire.

It will be understood that elements of any desirable length and shapemay be produced by the method of construction herein described and as itis common practice to braid cords of asbestos fibre around wires, thepresent types of machinery are available and the element may be producedat very low cost.

The invention as herein described is particularly applicable toresistance,elements for electric heating devices, but it must beunderstood that the particular manner of insulating an electricconductor by means of more than one covering of fibrous material,wherein the successive coverings are coated with a dielectric material,may be utilized for the insulation of electric conductor wires ofvarious kinds.

What I claim as my invention is:-

l. A method of insulating and permanently shaping an electricresistance. unit, consisting in braiding a covering of asbestos fibrearound the resistance element. applying a refractory in a plastic formto impregnate the filn'es of said covering and completely enclose sameleaving a substantial thickness overlying the braided covering, thenbraiding a second covering of fibrous material over the moist refractorycovering while the latter is still plastic, then applying a refractorymaterial in fiuid form to the exterior of said outer fabricated coveringto impregnate the fibres thereof. then bending the composite member soformed bodily while the refractory is in a soft plastic form to adesired configuration. then dry- I ing the moisture therefrom andfinally baking the refractory material at a refractory fusingtemperature to bond the same with the respective braided coatings andrigidly preserve the shape into which said composite member has beenbent.

2. A method of forming an insulated electrl conductor, consisting inpreparing continuous strands of asbestos fibre and cotton threads, thenbraiding same around the conductor forming a covering of part asbestosand part cotton, then applying a refractory material in plastic form toimpregnate the fabricated structure, then covering the impregnatedstructure with a second covering of fibre strands, then impregnating theouter covering with a refractory material in plastic form, then dryingthe moisture from the produced article, and finally burning out thecotton fabric and fusing the refractory material forming a rigid bondbetween the remaining asbestos fibres of said covers.

3. A method of forming a rigid configurated insulated resistance heatingunit comprising first Qenvelopingalengthofresistancewireinastrandaisaeos ed fibrous sheathtreated with a refractory in fiuid or plastic form, then distorting thewire and envelope thereof while the refractory is still in plastic formto shape the unit to the required configuration, and finally baking theshaped unit to permanently set the refractory-treated sheath and retainthe unit permanently in shape.

4. A method of forming a rigid configurated insulated resistance heatingunit comprising first braiding a fibrous coating about a coiledresistance wire and impregnating same with a refractory capable of beingfused only at a temperature higher than the normal operating temperatureof the resistance unit to form a hard refractory shell thereabout, thenpre-shaping the thus treated wire bodily while the refractory is stillplastic to form a unit of the desired configuration, and finally bakingthe thus shaped unit at a temperature sufilciently high to fuse therefractory and permanently set the same and retain the unit rigidly inshape.

5. A method as claimed in claim 4 in which the coated resistance wire isbent into a double loop configuration having one loop nested within theother and all of said loops being disposed in a common plane after whichthe unit is baked.

6. A method as claimed in claim 4 in which the refractory-treatedcoating and enclosed resistance element is made in long lengths andbefore baking is cut into shorter lengths, each short 1 length beingbent bodily into looped form with the ends adjacent, arranging a.refractory terminal block to bridge the end portions of the looped unitin contact with the plastic refractory thereof and with the ends of theresistance wire projecting therefrom, and finally baking the compositestructure to unite the refractory block with the refractory coating andpermanently set the unit to shape.

RAYMOND G. BRIDGES.

